The present invention relates to an image processing method and an apparatus that prepare treatment planning based on three-dimensional data obtained by making measurements on a patient using an X-ray computed tomography (CT) unit in treating diseases such as cancer with radiation. More specifically, the present invention is directed to an image processing method and apparatus adapted for radiotherapy treatment planning using digitally reconstructed radiographs (DRRs), which are permeation images generated from three-dimensional data obtained from a tomographic image measurement apparatus.
Treatment methods involving injection of beams of radiation such as X-rays and beams of protons onto a focus portion such as cancer are considered effective. To give a patient such a treatment, preliminary treatment planning must be prepared. A radiotherapy treatment is generally given under the following procedure.
First, part of a patient body including an affected part is measured using an apparatus such as an X-ray CT unit. The affected part is specified from the measured data, and its position and size are grasped. Then, the isocenter is set to the affected part, and conditions such as the direction of irradiation, number of injections and range of irradiation are simulated and adjusted so that radiation can be focused onto the affected part as closely as possible. Then, based on the results of the simulation and adjustment, markings are made on the patient body. Thereafter, the patient is requested to go to the radiotherapy treatment unit, positioned on the unit in accordance with the markings, and given the treatment.
At the time of the aforementioned simulation, a method of preparing treatment planning using DRRs is available. The DRR is a photographic image obtained by projecting onto a plane the pixels of data produced by a computed tomography unit such as an X-ray CT unit (these pixels will hereinafter be referred to as xe2x80x9cvoxelsxe2x80x9d) using radially expanding rays that are irradiated from a radiation source.
The treatment planning using DRRs provides the advantage that correct simulations can be made by calculating the radiograph of an affected part based on the same paths as those of the radiation beam provided by the actual treatment unit.
However, simple calculation of a radiograph imposes the problem that the transmitted body structure is hard to grasp. The following literature provide some (1) J. Galvin et al., xe2x80x9cThe Use of Digitally Reconstructed Radiographs for Three-Dimensional Treatment Planning and CT-Simulationxe2x80x9d, Int. J. Radiation Oncoloay Biol. Phys., Vol. 31, No. 4, pp. 935-942, 1995, and (2) JP-A-8-164217.
Such literature disclose DRR generation methods that use a lookup table for making CT value conversions to highlight a bone area serving as a landmark when a radiograph is calculated. The CT value conversions are made using a bone window or the like.
However, the conventional techniques are successful in improving the contrast of the bone area, but unsuccessful in generating a DRR having an area of interest highlighted more clearly. If clear highlighting is implemented, the user can prepare a more accurate treatment design. Further, while an exemplary method disclosed in JP-A-8-164217 involves an edge process to project an area such as a bone area clearly, the edge process is not specifically described. Thus, an effective edge process to enhance the contour using treatment data from an X-ray CT unit or the like must be developed.
Moreover, for treatment planning, measurements must be made with respect to the size of a target tumor and the size of an irradiation range. Since a DRR is a projected image formed by radially expanding rays, such measurements cannot be made on the DRR.
Furthermore, it takes much time to generate a DRR. Therefore, for interactive data processing, a high-performance computer is required, and this has prevented interactive processing with a low-performance computer.
To overcome the aforementioned problems, the present invention provides a unit for allocating color information so as to correspond to pixel values of three-dimensional data that is measured by an X-ray CT unit or the like, and allows a DRR to be generated by projecting the data using color information converted from the pixel values. In addition, the present invention provides a method of subjecting three-dimensional data that is measured by an X-ray CT unit or the like to an edge process based on a standard deviation, and allows a DRR to be generated by projecting the thus edge-processed three-dimensional data.
In the present invention, a position for projecting a DRR may be on a flat plane which includes an isocenter and which is perpendicular to a line connecting the isocenter to a radiation source. In the present invention, the user may specify the number of pixels and resolution of a DRR, and the sampling interval of voxels on a ray connecting a pixel on the DRR and the radiation source. Further, intermediate images of low resolution may be displayed until a final DRR is displayed.
As described above, the image processing method according to the present invention allows the user to clearly display and easily grasp an area of interest such as a bone structure and the contour and shape of organs by means of an edge process when the user prepares treatment planning based on a DRR, which is a radiograph, consisting of three-dimensional data gathered from a computed tomography unit such as an X-ray CT unit before a radiotherapy treatment is given to a patient.
Moreover, the image processing method according to the present invention allows the user to measure data on a flat plane of a DRR including the isocenter of an area of utmost interest when data such as the size of a target tumor and the range of irradiation are measured. Furthermore, the method allows the user to select image quality and speed. Since the user can roughly grasp the condition of the area of interest before obtaining a final, high-resolution DRR, the user is allowed to process data interactively by, e.g., changing the direction of irradiation in order to generate the final DRR with improved resolution and increased number of pixels.